LONDON (Reuters) - British Prime Minister Theresa May's gamble on a June 8 snap election was thrust into doubt after a Survation poll showed her Conservative Party's lead had dropped to a new low of just one percentage point.

While British pollsters all predict May will win the most seats in Thursday's election, they have given an array of different numbers for how big her win will be, ranging from a landslide victory to a much more slender win without a majority.

Some of the polls indicate the election could be on a knife edge that would throw Britain into political deadlock just days before formal Brexit talks with the European Union are due to begin on June 19.

In a sign of how much her campaign has soured just five days before voting begins, May's personal rating turned negative for the first time in one of ComRes's polls since she won the top job in the turmoil following the June 23 Brexit referendum.

Survation said the Conservatives were on 40 percent and Labour on 39 percent, indicating May's lead has collapsed by 11 percentage points over two weeks and that her majority was now in doubt.

"Prime Minister May's overall majority now hangs in the balance based on our most recent data," Survation founder Damian Lyons Lowe told Reuters. "The risk of May not having an overall majority has increased significantly based on our data."

The pollsters, though, indicated vastly different outcomes for May: ranging from a landslide majority of over 100 seats to a YouGov model which estimated that May would win 308 seats, too few for a majority in the 650-seat parliament.

Her party's lead over the opposition Labour Party was in a range of 1-12 percentage points, according to six polls published on Saturday. Four showed her lead narrowing, one showed her lead unchanged and one, ORB, showed it widening to 9 points from six.

ELECTION GAMBLE?

May called the snap election in a bid to strengthen her hand in negotiations on Britain's exit from the European Union, to win more time to deal with the impact of the divorce and to strengthen her grip on the Conservative Party.

If she fails to beat handsomely the 12-seat majority her predecessor David Cameron won in 2015, her electoral gamble will have failed and her authority will be undermined both inside the Conservative Party and at talks with 27 other EU leaders.

When May stunned political opponents and financial markets by calling the snap election, her poll ratings indicated she could be on course to win a landslide majority on a par with the 1983 majority of 144 won by Margaret Thatcher.

But since then, May's lead has been eroded, meaning she might no longer score the thumping victory over socialist Labour leader Jeremy Corbyn she had hoped for ahead of Brexit negotiations.

YouGov said May's lead was down to four percentage points, ICM said her lead had narrowed to 11 points from 14, Opinium said her lead had fallen to six percentage points from 19 points at the start of the campaign.

ComRes found the Conservative Party's lead stood at 12 percentage points, unchanged from a week ago but far below the 21-point lead it recorded just before she called the election on April 18.

The ComRes polling firm found May's personal net approval rating had fallen to minus 3, down 12 points from a positive 9 point approval rating in February. Corbyn's net personal rating was minus 15, up 18 points from a minus 33 score in February.

The Opinium poll for the Observer newspaper suggested May was set for a substantial parliamentary majority on June 8.

MAY'S CAMPAIGN

Just days before polls open, May's campaign sent conflicting messages on taxation for top earners, an issue which the Conservatives are sensitive about because the opposition Labour Party casts them as the party of the rich and privileged.

May insisted nothing had changed on her tax policy -- she has kept open the possibility of tax rises -- after her defence minister, Michael Fallon, was quoted by a national newspaper as saying that income tax would not increase for higher earners.

"Our position on tax hasn't changed," May said while on a visit to West Yorkshire in northern England.

Her comments were echoed by her finance minister, Philip Hammond, though May has stoked speculation about Hammond's future by refusing to say whether she will reappoint him if she wins the election.

Labour leader Corbyn, who has run an unexpectedly strong campaign, said the Conservative leadership was in disarray.

The decline in support for the Conservatives coincided with a surprise announcement by May last month that she would make elderly people pay more for their social care, despite concerns that it could undermine support among ageing, wealthy homeowners - a core source of Conservative votes.

May later backtracked on the proposal but grew irritated at suggestions she was backing down and repeatedly insisted to reporters that "nothing has changed".

Campaigning was suspended for several days after a suicide bomber killed 22 people at a concert in Manchester on May 22.